For the past 45 years, there has been a great deal of debate regarding the health issues surrounding the fluoridation of public water supplies. Recent ecological studies demonstrating a positive association between fluoridation and hip fracture have rekindled the debate (Jacobsen et al., Danielson et al.). Both of these studies, however, were conducted at the aggregate level and are subject to the ecologic fallacy. In order to accurately evaluate the association between community water fluoridation and osteoporotic fractures, research must be conducted on the individual level where confounders such as hormone replacement therapy and actual fluoride exposure can be measured. The purpose of this study is to evaluate the association between fluoridation and osteoporotic fractures while controlling for all known confounding variables. The study population will consist of women enrolled in the NIH supported multi- center Study of Osteoporotic Fractures (SOF). During 1986-88, slightly more than 9,700 women (greater than or equal to 65 years) were enrolled in the SOF study at four sites; Portland, OR; the Monogahela Valley, PA; Baltimore, MD; and Minneapolis, MN. Approximately 7,500 women have taken part in four extensive examinations over a five-year period. The SOF database contains information on all known confounding variables, bone mineral density at multiple sites, and fracture rates. The database for the Monogahela Valley also contains information on fluoride exposure via water systems for each of the participants from 1950-1990. During the course of this study, data on fluoride exposure from water systems will be gathered from the women participating in SOF at the Portland, Baltimore, and Minneapolis study sites. Baltimore and Minneapolis have been fluoridated since 1952 and 1957 respectively, while Portland and the majority of the Monongahela Valley are not fluoridated. The primary goal of the study will be to determine if fluoride exposure status is associated with fracture incidence rates, bone mineral density, and/or the rate of bone loss on the individual level once confounding variables are controlled for. Given that the USPHS promotes fluoridation of water at 1.0 ppm to prevent dental caries, the effect of consuming such water on osteoporotic changes needs to be clarified.